Polyether polyols are useful as intermediate in the preparation of polyurethanes. In addition, polyether polyols are commonly used directly in other applications and may be employed as functional fluids and surfactants, for example.
Typically, polyether polyols are prepared by polymerizing a mono- or unsubstituted alkylene oxide such as ethylene oxide, propylene oxide, or 1,2-butylene oxide using base catalysis or by polymerizing an oxolane such as tetrahydrofuran using acid catalysis. The properties of the polyether polyols may be controlled by varying the chemical structure of the monomers, the order and arrangment of the monomers in the polyol, the polyol molecular weight, and the average functionality of the polyol.
To date, only a limited variety of polyether polyols containing isobutylene oxide, a di-substituted alkylene oxide, have been prepared. This is due to the difficulties associated with polymerizing this monomer while retaining control of molecular weight and end-group functionality.
U.S. Pat. No. 3,374,277 teaches crystalline, high-melting isobutylene oxide diols having a molecular weight of 500 to 20,000. The diols are obtained by the alkyl lithium promoted cleavage of very high molecular weight isobutylene oxide homopolymers. The predominantly head-to-tail arrangement of the isobutylene oxide units in the high molecular weight homopolymers and the mechanism of cleavage result in the diol products having approximately 50% tertiary hydroxyl end-groups and 50% primary hydroxyl end-groups. It is well-known that tertiary hydroxyl groups are much less reactive towards electrophilic functional groups such as isocyanates than are primary or secondary hydroxyl groups. Thus, the isobutylene oxide diols taught by this reference would be difficult to incorporate into polyurethane using conventional methods and techniques, since chain extension will be slow compared to polyols containing predominantly primary or secondary hydroxyl end-groups. Furthermore, precise control of molecular weight and molecular weight distribution is difficult using this method due to the random nature of the cleavage process. Isobutylene oxide polyols having a functionality (average number of hydroxyl groups per polymer chain) higher than two cannot be prepared by the process taught in this reference.
EP No. 173,879 teaches polyether polyols having an internal block of a mono-substituted alkylene oxide such as propylene oxide and an end-cap consisting of a limited number of isobutylene oxide monomer units. These polyols have only tertiary hydroxyl end-groups, which, for the reasons discussed previously, are normally undesirable when formulating polyurethanes.
An object of the present invention is to provide isobutylene oxide polyether polyols which cannot be made by prior processes.
More specifically, an object of the invention is to provide polyether polyols having internal blocks comprised of either isobutylene oxide or a random mixture of isobutylene oxide and a mono- or unsubstituted alkylene oxide and having one or more endcaps of a mono- or unsubstituted alkylene oxide to provide primary or secondary hydroxyl groups reactive with electrophilic functional groups.
A further object of the invention is to provide a process for producing such isobutylene oxide polyether polyols which is relatively straight forward and permits good control of polyol molecular weight, molecular weight distribution, composition, functionality, and physical and chemical properties.